Session G07: Biofluids: Biofilms

An experimental study on the effect of respiratory fluid composition on bacterial viability and deposit adhesion characteristics

This study investigates the impact of respiratory fluid composition on the viability of pathogens and the adhesive properties of deposits formed when the surrogate respiratory fluid droplets dry on surfaces. Given the potential threat of respiratory fluid-containing pathogens to human health, understanding the conditions under which deposits form and the state of the pathogens within them is crucial. Clinical research has shown that salt ions and mucin are the primary components of respiratory fluid, which can vary significantly depending on the individual's pathological conditions. The study demonstrates that variations in salt and mucin content in respiratory droplets have a significant effect on the viability of pathogens and the adhesive properties of the deposits. To understand the underlying factors influencing viability and adhesion, the researchers examine the dynamics of evaporation, internal flow, and precipitation. Additionally, the characteristics of the deposits are analyzed using optical profilometry, scanning electron microscopy, and atomic force microscopy, while pathogen distribution is investigated using confocal microscopy.   

Development of a field instrument to quantify frictional drag of a heterogeneous biofilm

The presence of a relatively low form biofilm has been shown to significantly increase power requirements and resulting greenhouse gas (GHG) emissions from shipping. The International Maritime Organization has set ambitious goals in reducing GHG emissions from international shipping by at least half in 2050 compared with 2008. One of the main ways to inhibit biofilm growth and resulting GHG emissions is through proper coating selection. There are numerous test sites and testing campaigns whose purpose is to evaluate various coating types to identify top performing coatings and underlying formulations. The performance of these coatings is typically determined through visual inspection. Determining the equivalent sand grain roughness (k_s) of the test panels would allow for a direct comparison of the frictional drag of the surfaces and aid in the development of numerical methods quantifying frictional drag of biofilms on full-scale ships. The present work investigated the feasibility of a field deployable instrument that could determine the frictional drag and resulting k_s values of coating test panels immersed in a marine environment with a heterogeneous biofilm. Several sources of uncertainty where examined: 1) flow asymmetry due to the presence of a smooth wall (instrument) and rough wall (biofilm/coating), 2) flow development length, and 3) streamwise heterogenous roughness of the biofilms. The effects of these elements on the overall principal dimensions of the instrument are discussed. Results from this instrument, namely equivalent sand grain roughness of 220 and 500-grit sandpaper and a surface with a light biofilm, are compared with previous work reported in the literature.   

A multiscale mathematical model for biofilm structure and viscoelasticity

Biofilms are initiated by individual polymer-producing bacteria in aqueous that undergo a phenotypic switch and produce various types of extracellular polymeric substances (EPS). The EPS form a polymeric network combined with the fluid solvent creating a gel-like fluid that exhibits rheological behavior. We developed a mathematical model to study this complex heterogeneous system across different scales. First, we implemented a linear viscoelastic model to describe the biofilm viscoelastic response during a creep-recovery test. Then, using a Bayesian framework, we estimated the viscoelastic parameters and quantified the uncertainty in their estimation for three different Pseudomonas aeruginosa biofilm variants at different stages of formation based on experimental data. Finally, we modeled the spatiotemporal organization of biofilm composition as a multi-phase system where each volume in space is fractionally occupied by the polymeric network and the fluid solvent. Each fluid moves with its own velocity, and the difference in velocities develops a drag force between the phases, coupling the mechanics. We formulated the motion and interaction of these components as a set of equations in an incompressible Navier-Stokes form. This model helps us understand the motion of the biofilm components and can help future research works elucidate the dynamics of polymeric network that forms the backbone of the biofilm.   

Drag generation mechanisms of artificial hairy biofilm-like surfaces

Hard and soft biofouling formation on naval objects has been shown to increase drag and cause performance deterioration. Understanding the drag generation mechanisms of soft biofouling is complicated due to the unconstrained nature of biofilm growth and the resulting non-uniform variations in the surface topologies among different trials. Studying hydrodynamic drag generation of biofilms in a laboratory setting is challenging due to inhomogeneities in geometry along the surface and sloughing during data collection. To isolate the effect of fouling geometry, the drag producing mechanism of artificial biofilm-like hairy surfaces is studied using a skin-friction flow test facility. Skin-friction coefficients of the compliant biofouling-like surfaces and their rigid replicas are estimated and compared. Interaction of the surfaces with the underlying flow is observed and compared using high-speed videos.